<template>
  <div class="pagination">
    <button :disabled='pageNo==1' @click="$emit('getPageNo', pageNo-1)">上一页</button>
    <button v-if="satrtNumAndEndNum.start > 1" @click="$emit('getPageNo', 1)" :class="{active: pageNo==1}" >1</button>
    <button v-if="satrtNumAndEndNum.start > 2">···</button>
    <!-- 中间部分 -->
    <button v-for="(page, index) in pages" :key="index" @click="$emit('getPageNo', page)" :class="{active: pageNo==page}">{{ page }}</button>
    
    <button v-if="satrtNumAndEndNum.end < totalPage - 1">···</button>
    <button v-if="satrtNumAndEndNum.end < totalPage" @click="$emit('getPageNo', totalPage)" :class="{active: pageNo==totalPage}">{{ totalPage }}</button>
    <button :disabled='pageNo==totalPage' @click="$emit('getPageNo', pageNo+1)">下一页</button>
    
    <button style="margin-left: 30px">共 {{ total }} 条</button>
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    props: ['pageNo', 'pageSize', 'total', 'continues'] ,
    computed: {
      // 总共多少页，向上取整
      totalPage() {
        return Math.ceil(this.total/this.pageSize)
      },
      // 计算连续的页码的起始数字与结束数字
      satrtNumAndEndNum() {
        // 解构出连续的页码数、当前页、总的页码数
        const {continues, pageNo, totalPage} = this
        let start = 0 , end = 0
        // 总页数少于连续页码数的情况
        if(continues > totalPage) {
          start = 1
          end = totalPage
        } else {
          // 正常现象：总页数大于连续页码数的情况
          start = pageNo - parseInt(continues/2)
          end = pageNo + parseInt(continues/2)
          // 特殊情况：start小于1的情况
          if(start < 1) {
            start = 1
            end = continues
          }
          // 特殊情况：end超过总页码的情况
          if(end > totalPage) {
            start = totalPage - continues + 1
            end = totalPage
          }
        }
        return{start, end}
      },
      // 计算中间部分起始数字与结束数字的数组，之后再渲染
      pages() {
        let pages = []
        let count = 0
        let i = this.satrtNumAndEndNum.start
        while(i <= this.satrtNumAndEndNum.end) {
          pages[count] = i
          count++
          i++
        }
        return pages
      }
    }
  }
</script>

<style lang="less" scoped>
  .pagination {
    text-align: center;
    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }
</style>
